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Metallurgical Analysis - Comparing
Steels for Katanas
The objective for the Japanese katana was to create the best balance
possible between toughness (for impact absorption) and hardness (for the
cutting edge - after all, you can only cut through things that are
relatively softer than your edge). These properties, hard and soft, are
inversely proportional! In terms of aesthetics, one of the most visible
aspects of the Japanese sword is the hamon, which is the cloud-like
temper line which is the intersection between the different molecular
makeups of the steel that make up the hardened edge and the softer body.
Achieving the balance between toughness and hardness is a result of heat
treating, and different steels will respond differently to heat treating.
Consequently, certain steels can take a beautiful hamon whereas on
other steels the hamon is less visible.
Many thanks to Randal Graham of Dragon Fist Forge for providing his input
and experience with the following table:
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What is the ideal modern steel to use for a Japanese style katana? This
article, like our | AISI 1050 | - | Makes excellent swords if you keep within the Rc 57-58 range for the edge. Allowing for a fantastic hamon, AISI 1050 is a great steel for teaching and practice, and can result in super-tough blades. It's carbon content isn't as high as I would like. Blades made from 1050 can sport fair edge-holding capabilities. In maintaining a Rc 60 edge, the steel may have a tendency to be brittle. Countering the brittleness, anything more than a light stress-relief will dip the hardness to low. |
| AISI 1060 | - | This can be considered a good baseline steel for katanas. Allows for a great hamon. Differentially hardened, this steel is superior for a katana whose main requirement is toughness. |
| AISI 1070 and 1084 | - | In the case of these steels, the hamon will be a little more defined though not as flashy. These steels can be just as tough as 1060 but must be heat-treated very carefully. Due to its exacting and strict requirements to achieve good results in a heat treat, 1070 and 1084 are not the best recommendations for katanas. However, with the use of salt baths to aid in the heat treating process, I've seen them outperform 1060. However, it's also very easy to foul up in the hardening process. AISI 1070 and 1084 can be unforgiving steels! |
| AISI 1095 | - | For practical reasons, AISI 1095 can be treated the same as 1084, but it may have a higher tendency of cracking during the quenching process. At 0.9% carbon, this steel has more carbon content than the idea 0.8% maximum or level that allows for the steel to harden fully. AISI 1095, thus, may mean added expense due to so many potential points of failure. (Editor's note: The Shinto Katana by Paul Chen reportedly uses 1095, which may explain the high Rc 60 readings that Hank Reinhardt of MRL gets from the edge of the swords.) |
| AISI 5160 | - | A great steel all around, but not very "hamon-friendly" in appearance, as this steel does not react the same way to a traditional clay coat as the simpler AISI 10XX series steels will. In testing, it was common for a small crack to start and for the whole edge to break away from the body! This steel seemed to like through-hardening much better, and in that situation it is pretty hard to beat. |
| L6 | - | L6 is a difficult steel to work with, with many trade-offs, however. Although it responds better to differential hardening than 5160, it has a fairly under-whelming hamon, is prone to rusting, and needs more control in the hardening than the previously listed steels. |
| D2 | - | If stainless properties and low maintenance is a requirement, then D2 may be an answer. However, the edge hardness has to be reduced to around Rc 55. The steel must be treated properly. In comparison with A2 tool steel, I would personally choose D2 over it. Due to its high alloy content, there is no proper way of differentially hardening steels like A2 or D2 in a way that provides for high quality results. (Editor's note: D2 contains chromium, but not enough to qualify it as a stainless steel - considered unsuitable for swords altogether. The chromium level, at higher contents, weakens the molecular bonds in steel, so it's good for short lengths only. The chromium content is countered by the presence of molybdenum.) |
| A2 | - | A2 is a tool steel that is commonly used by some makers of Westernized Interpretations of the Japanese Katana. The logic is that a steel used to cut through other steels is probably a good sword steel. However, the requirements for Japanese swords is that it must be differentially hardened, and the only way to do so with air-hardening A-2 and give it a harder edge is an inelegant process of running a torch along the edge to make it hot - often quipped as "zone hardening" in marketing these swords. This is pushing the limits of good heat-treating techniques. Given that A2 is a high alloy steel with stringent requirements, this "zone hardening" is partial hardening at best. |
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Forge-welded or Folded Cable Steel | - | Cable-welded and folded steel cable verified at 0.9 % carbon is fantastic for a traditional looking sword, with performance parameters on par with that of traditionally made katanas. Carbon loss is figured into the equation during the welding/forging process. I aim for a final content of about .75 or thereabouts. Of course, it's more labour to fold and weld (the price goes up) and such a sword should have a good polish performed on it to bring out all aesthetic details. |
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